Add Braintree to Gemfile.
Modified user model, added braintree initializer, and added braintree id to user table migration.
Added Braintree Environment variable handling to h.sh.
Merge branch develop into branch braintree.
Update README and refactor User model. Add BrainTreeRails initializers.
Remove call to tag_helper_ext from https://github.com/lyang/braintree-rails-example/blob/master/lib/rails_ext/tag_helper_ext.rb